1. Field of the Invention
This invention resides in the field of specimen sampling equipment and liquid handling equipment in general for automated analyzers, with particular attention to racks in which sample tubes are held in such an analyzer.
2. Description of the Prior Art
Laboratory analyzers for the automated analysis of a multitude of biological specimens typically include several coordinated liquid transfer systems and one or more movable sample tube racks. These racks hold the sample tubes in position and transport them to each of various positions in the analyzer where different robotic mechanisms are used for liquid addition and withdrawal in the performance of the different functional operations of the analysis. The optimal rack is one that holds the tubes in a stable manner, thereby preventing the tubes from becoming dislodged or their orientation from being changed as the rack is moved within the analyzer, and also one that aligns the tubes properly for the robotics in the analyzer. The optimal rack should not be limited to any particular tube size but should instead accommodate tubes of different sizes while maintaining proper alignment of each tube regardless of size.
Among the specimen racks of the prior art are those that contain a row of individual tube chambers that are circular in cross section. Each chamber has a single set of spring arms extending from the upper rim of the chamber downward and inward toward the chamber axis to hold the tube in place during movement of the rack. Even with four spring arms distributed around the circumference of the chamber, the tube orientation is only secured at one location along the height of the tube, and the range of tube diameters that the chamber can accommodate is limited. The rack also suffers from costly construction since the spring arms have a V-shaped cross section and are angled at each end toward the vertical. Contributing further to the cost are the fact that the spring arms are constructed as components separate from the body of the rack, the spring arms being metallic and the body itself being of plastic construction. In the assembled rack, the metal spring arms are fitted into the body but susceptible to slippage and potential disengagement.